|Publication number||US7253633 B2|
|Application number||US 10/910,819|
|Publication date||Aug 7, 2007|
|Filing date||Aug 5, 2004|
|Priority date||Aug 15, 2003|
|Also published as||EP1664809A1, US20050036249, WO2005019845A1|
|Publication number||10910819, 910819, US 7253633 B2, US 7253633B2, US-B2-7253633, US7253633 B2, US7253633B2|
|Inventors||Ronald C. Harvey|
|Original Assignee||Northrop Grumman Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (12), Referenced by (2), Classifications (10), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates generally to ground fault detectors and more particularly to ground fault detectors in polyphase power systems.
Polyphase power systems are designed to supply electrical power to a balanced system load. A failure of a connection may cause power to be diverted to a grounded surface and result in a ground fault. Ground fault detectors provide an indication of an existence of leakage currents associated with the ground fault. Transient leakage currents are created when equipment powered by the polyphase power system is turned on or off. When equipment is turned on or off, ground fault detectors may incorrectly indicate a ground fault. The incorrect indication of a ground fault undesirably wastes time for technicians who consequently must attempt to discover the cause of the indicated ground fault.
Thus, a need exists for an increase in accuracy of ground fault detection for a polyphase power system.
The invention in one implementation encompasses an apparatus that comprises a fault detection component that employs one or more voltage dividers to promote an accuracy for adjustment of a threshold that is employable for a determination of an existence of one or more ground fault conditions in one or more of a plurality of power lines. A polyphase power system with a system safety ground supplies a plurality of power phases over the plurality of power lines, respectively, to power a load.
Features of exemplary implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which:
The phase terminals 208, 210, and 212 are coupled with an ungrounded delta-connected generator of the polyphase power system 202. The power status component 102 in one example comprises a neutral terminal 214 coupled with a system safety ground from the polyphase power system 202. The phase terminal 208, phase terminal 210, and phase terminal 212 comprise power phases that are separated by one hundred and twenty degrees. The phase terminals 208, 210, and 212 comprise a line-to-line voltage between another of the phase terminals 208, 210, and 212 and a line-to-ground voltage between the neutral terminal 214. The line-to-line voltage is equal to the line-to-ground voltage times the square root of three when the load on the lines is balanced, as will be appreciated by those skilled in the art.
The power status component 102 in one example comprises one or more fuses 216, 218, and 220 and one or more power indicator components 222, 224, and 226. The power status component 102 employs the fuses 216, 218, and 220, to protect the phase terminals 208, 210, and 212, respectively. The power status component 102 in one example employs the power indicator components 222, 224, and 226 to provide an indication of power across the phase terminals 208, 210, and 212. The power indicator components 222, 224, and 226 in one example comprise a neon lamp 228 and a diode 230. When a voltage differential exists between two phase terminals, the neon lamp is lit, indicating that there is power across the phase terminals, as will be appreciated by those skilled in the art. In one example, the power indicator 222 indicates presence of the line-to-line voltage across the phase terminals 208 and 210, the power indicator 224 indicates presence of the line-to-line voltage across the phase terminals 208 and 212, and the power indicator 226 indicates presence of the line-to-line voltage across the phase terminals 210 and 212.
The power status component 102 in one example comprises one or more test terminals 232, 234, 236, and 238 and one or more resistors 240 for providing test points of the phase terminals 208, 210, 212, and the neutral terminal 214, respectively. The power status component 102 in one example comprises an alternating current to direct current converter 242 that employs the phase terminals 208 and 210 and the neutral terminal 214 to create one or more direct current terminals 244 and one or more localized grounds 246. The direct current terminal 244 in one example supplies a voltage of five volts.
An illustrative description of exemplary operation of the phase fault detector 306 is presented, for explanatory purposes. The line-to-line voltage of the phase terminals 208, 210, and 212 in one example comprises 120 Volts. A resistor 310 provides a phase reference from the phase terminal 212 to the localized ground 246. The localized ground 246 is coupled with the neutral terminal 214 by a capacitor 311. A diode 312 and a resistor 314 allow a positive cycle of the line-to-ground voltage of the phase terminal 212 to charge a capacitor 316. The capacitor 311 provides a reference to the neutral terminal 214. Unbalanced leakage currents will flow into the safety ground at the system load. In a balanced load condition, there is no potential difference between the neutral terminal 214 and the localized ground 246, thus no current will flow through the capacitor 311. On unbalanced loads an AC current will flow through the localized ground 246. The capacitor 311 will smooth these currents providing essentially a DC offset on the localized ground 246 relative to the neutral terminal 214. This oftset affects a low voltage threshold sensitivity of the phase fault detector 306. The ratio of impedance of the capacitor 311 to impedance of the capacitor 316 affects sensitivity levels of the phase fault detector 306. For example, the capacitor promotes an adjustability of the sensitivity of the detection of ground fault condition. The capacitor 316 in one example is charged to approximately the peak line-to-ground voltage of the phase terminal 212 and discharges approximately ten percent between peaks.
Two or more resistors 318 and 320 serve to provide a voltage divider for the line-to-ground voltage of the phase terminal 212. For example, the resistors 318 and 320 provide a divided voltage to a comparator component 322. The comparator component 322 in one example comprises an operational amplifier circuit as a comparator. The comparator component 322 in one example compares the divided voltage with the reference voltage to determine if the line-to-ground voltage is above a given threshold. In one example, the reference voltage comprises a voltage of 1.2 volts. When the divided voltage is greater than the reference voltage, then the line-to-ground voltage is within an acceptable level. The threshold can be adjusted by changing the resistance of the resistor 320. For example, a lower resistance of the resistor 320 will increase the threshold of the comparator. When the divided voltage is greater than the reference voltage, the operational amplifier of the comparator component 322 supplies a voltage across a resistor 324 and a light-emitting diode 326, causing the light-emitting diode 326 to turn “ON.” When the divided voltage is less than the reference voltage, the operational amplifier of the comparator component 322 supplies no voltage to the light-emitting diode 326, and the light-emitting diode 326 turns “OFF.” The phase fault detectors 302 and 304 function analogously to the phase fault detector 306.
The fault indicator 308 in one example is electrically connected with the phase fault detectors 302, 304, and 306. When one or more of the line-to-ground voltages of the phase terminals 208, 210, and 212 drops below the given threshold, the fault indicator 308 turns a light-emitting diode 328 “ON.” For example, the phase fault detectors 302, 304, and 306 comprise green light-emitting diodes, and the fault indicator 308 comprises a red diode. Under normal operating conditions with no faults detected, the green light-emitting diodes are “ON” and the red light-emitting diode is “OFF.” Once a fault is detected on one or more of the phase terminals 208, 210, and 212, the corresponding green light-emitting diode turns “OFF” and the red light-emitting diode turns “ON.”
The steps or operations described herein are just exemplary. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.
Although exemplary implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.
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|JP2000308254A||Title not available|
|RU2155424C1||Title not available|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7821414 *||Dec 28, 2007||Oct 26, 2010||Hong Fu Jin Precision Industry (Shenzhen) Co., Ltd.||Polyphase source detecting circuit|
|US20090051555 *||Dec 28, 2007||Feb 26, 2009||Hong Fu Jin Precision Industry (Shenzhen) Co., Ltd.||Polyphase source detecting circuit|
|U.S. Classification||324/509, 324/512, 324/522, 324/521, 361/42|
|International Classification||G01R31/02, H02H3/00, G01R31/08|
|Aug 5, 2004||AS||Assignment|
Owner name: NORTHROP GRUMMAN CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HARVEY, RONALD C.;REEL/FRAME:015664/0135
Effective date: 20040803
|Aug 21, 2006||AS||Assignment|
Owner name: LITTON SYSTEMS, INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:NORTHROP GRUMMAN CORPORATION;REEL/FRAME:018148/0388
Effective date: 20060621
|Jan 7, 2011||AS||Assignment|
Owner name: NORTHROP GRUMMAN SYSTEMS CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:NORTHROP GRUMMAN CORPORATION;REEL/FRAME:025597/0505
Effective date: 20110104
|Feb 3, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Jan 29, 2015||FPAY||Fee payment|
Year of fee payment: 8